1. Field of the Invention
The present invention relates to vehicle suspension mechanisms and more particularly to vehicle rear suspension mechanisms. More specifically, the present invention pertains to a vehicle rear suspension mechanism in which a toe-in displacement is produced in an outboard rear wheel under a transversely inwardly directed side force.
2. Description of the Prior Art
In general, vehicle rear wheels are subjected, when the vehicle is running through a curved path, to a side force which is directed toward the center of curvature. In order to obtain a steering stability in an operation through a curved path, various proposals have been made to make use of such side force to produce a toe-in displacement in a rear wheel, particularly, in an outboard rear wheel located outwards from the other wheel with respect to the center of curvature, so that an over steering can effectively be prevented. For example, German patent specification No. 2,158,931 discloses a vehicle rear suspension including a rear suspension arm having one end mounted on a vehicle body member for vertical swinging movements and the other end connected with a wheel hub which in turn carries a rear wheel for rotation about its own axis. The connection between the suspension arm and the wheel hub is such that the wheel hub is connected to the arm by means of a vertically extending pivot pin which is located rearwards of the axis of the wheel and a spring which is disposed forwardly of the wheel axis between the wheel hub and the suspension arm. Thus, when the wheel is subjected to an inwardly directed side force, the spring is deflected and a toe-in displacement is produced in the wheel about the joint pin. German patent specification No. 2,355,954 proposes in this type of rear suspension mechanism to vary the spring force in accordance with the side force.
Japanese patent publication No. 52-37649, which corresponds to German patent application No. P 2200351.6, discloses a vehicle rear suspension including a rear suspension arm having one end swingably connected with a vehicle body member and the other end connected with a rear wheel hub. Between the suspension arm and the wheel hub, there are provided a pair of longitudinally spaced resilient members which can deflect in the transverse direction. The forward resilient member has a coefficient of resiliency which is smaller than that of the rearward resilient member so that a longer deflection is produced under a side force in the forward resilient member than in the rearward resilient member producing a toe-in displacement in the rear wheel. Further, there is described in the Japanese patent publication that a toe-in displacement of the rear wheel is also produced under a braking force by placing the center of displacement transversely outwardly of the central plane of the rear wheel.
It should, however, be noted that the aforementioned structures relate only to sideward deformations of springs or resilient members for producing the toe-in displacements so that the side force cannot effectively be utilized. Further, the structures are not designed to produce a toe-in displacement under a force transmitted through a drive axle such as a driving torque or an engine brake force. Moreover, the cited German patent applications do not deal with the subject matter of producing a toe-in displacement under a wheel braking force.
None of the prior art devices provide a rear-suspension system which can cause the rear tires to toe in even when braking forces are exerted thereon through operation of the brake pedal or by the engine-brake effect. The ability of the rear-suspension system to always cause the tires to toe in ensures proper driving stability during cornering. The toe-in ability of the rear-suspension is also desirable from the viewpoint of the stability of the vehicle during straight travel at a high speed which is particularly required in the case of a sports car.
Actually, roads are not completely flat but inherently have bumps and recesses of various sizes which act on the tires as external disturbances in various directions. Further, winds impinging upon the vehicle body in various directions also act on the tires as external disturbances in various directions, and in particular, side winds act on the tires as lateral forces. If the rear-suspension can maintain its toe-in ability even when these external disturbances are exerted on the tires, an understeer condition of the vehicle is always ensured, whereby the vehicle can always be stabilized. The external disturbances act as the lateral force, braking force or driving force described above irrespective of their origins.
Therefore, the rear-suspension system should toe-in against any one of the lateral force, braking force (due either to operation of the brake pedal or the engine-brake effect), and driving force. The lateral force is typically a thrust load produced during cornering and comprises a force acting on the treading point of the tires from outside to inside. The braking force due to operation of brake pedal comprises a force acting on the treading point of the tires from front to rear while the braking force due to the engine-brake effect comprises a force acting on the wheel center of the tires from front to rear. The driving force comprises a force acting on the wheel center from rear to front.
Thus, there is a need for a rear-suspension system that is capable of toe-in against any one of the lateral force, braking force, and driving force. The present invention is directed toward filling that need.